1. Field of the Invention
The present disclosure relates to fatigue testing of material specimens, and more specifically to apparatuses and methods for in-situ fatigue testing of material specimens under high fluid pressure conditions.
2. Description of the Related Art
Hybrid fuel cell/electric vehicles convert the chemical energy of hydrogen gas into electrical energy to power the vehicle's electric motor. In order to make these vehicles a viable for everyday transportation, decentralized hydrogen filling stations are needed to ensure hydrogen is available where consumer-demand is. In order for economic distribution, hydrogen must be piped from its point of production to its point of demand. An extensive pipeline infrastructure is thus needed to distribute the hydrogen from the generation plants to the filling stations.
The ASM Materials Handbook lists five specific types of hydrogen induced damage to metals and alloys. These types are: hydrogen embrittlement, hydrogen-induced blistering, cracking from precipitation of internal hydrogen, hydrogen attack, and cracking from hydride formation. Except for hydrogen embrittlement, a phase transformation is coupled to each of the listed hydrogen damages. Hydrogen embrittlement is the result of hydrogen atoms diffusing through the surface of certain materials. The hydrogen atoms can accumulate within the material's microstructure causing increased subsurface pressure and eventually cracks to form. Hydrogen embrittlement is a major concern for hydrogen pipeline material designers, since even a small leak in a pipe wall, a welded connection, a flange or a fastener could lead to a dangerous situation.
Fatigue effects in materials due to hydrogen contact may cause defects which can remain undetected until a catastrophic failure occurs without warning. Applying tensile, compressive, low cycle fatigue and high cycle fatigue loads to characterize the strength of materials is known. Novel apparatuses and techniques for testing materials under adverse conditions such as hydrogen gas contact are presently needed.